The invention relates to a device for a relative angular adjustment between at least two shafts (especially a crankshaft and at least one camshaft) connected to one another in a driving relationship. The camshaft, at its end on the driving side, carries an actuating element which is axially shiftable on this end and is connected positively to it via a helical gear teeth set. The actuating element is connected axially shiftable and fixed rotatively to a cylindrical hollow shaft surrounding it via a further helical gear teeth set. The hollow shaft carries a driving wheel of the crankshaft.
German Offenlegungsschrift No. 3,126,620 shows a device for varying the phase setting between an engine shaft and a control shaft in engines having two separate shafts for controlling engine inlet valves and outlet valves. This device provides for alternating between two different drive control settings. Each of the two control settings corresponds to one end position of a movable drive member which is connected to an engine shaft and a control shaft via couplings. At least one coupling is equipped with a helical teeth and by an axial shaft, causes a rotation of the control shaft in relation to the engine shaft. The adjustment of the drive member into one of the end positions is obtained by means of the pre-stress of a spring, while the adjustment into the other end position takes place in response to the pressure of oil from the engine-oil circuit. A centrifugally actuated slide assumes three different positions as a function of the engine speed wherein it correspondingly opens and closes oil flow bypass bores and thereby controls the oil pressure to the drive member. One position of the slide opens an oil bypass bore, below a specific engine speed, whereupon only a spring force acts on the drive member to keep the drive member in an end position
If the engine speed exceeds this first specific engine speed threshold value, the slide closes off the oil flow bypass bore as a result of the change of centrifugal force and the drive member is shifted axially into a second end position, counter to the spring stress, by means of the increasing engine-oil pressure. Here a relative rotation between the engine shaft and control shaft takes place and a control setting matched to this engine operating state is obtained thereby. After a further threshold value for the engine speed has been exceeded, the slide is moved into a position which once again allows an oil to flow bypass. The drive member is once more moved back into its first end position by means of the spring force and with a corresponding relative rotation. The adjustment of the drive member when the engine speed falls below the threshold values takes place in the same way.
The disadvantage of this device is that the control is carried out via the engine-oil circuit. At low engine speeds, for example during idling, the oil pressure is too low to be capable of causing an adjustment. Consequently, the drive member has to be brought into the position corresponding to this operating state by means of spring force. However, at a low engine speed and consequently a low oil pressure, such a spring force can prevent an adjustment of the drive member by means of pressure oil in the periods when there is an inhibiting camshaft torque, so that an adjustment can take place only during a driving camshaft torque, i.e. intermittently. To avoid the undesirable return of the drive member caused by the spring force together with the camshaft torque, the helical gear teeth must be made self-locking, i.e. with a low helix angle. Such a helix angle only allows for a short adjustment travel (i.e. the relative angular adjustment between the engine shaft and control shaft or camshaft) and therefore the variation of the control shaft is only slight.
Another disadvantage with such a device is that it is only possible to switch to and for between two end positions, although it is desirable to have the possibility of ensuring a continuous adjustment of the camshaft through many relative positions.
German Offenlegungsschrift No. 3,342,905 shows a device for a relative angular adjustment between two shafts connected to one another in driving terms. The device consists of two planetary gears which are arranged in a housing and the sun wheels of which are connected respectively to the drive shaft and to the output shaft. The torque transmission takes place via the planet wheels. The ring wheel of the planetary gear connected to the output shaft is connected fixedly in terms of rotation to the housing, while the ring wheel of the planetary gear located on the drive side can be rotated in the two directions of rotation by means of a stepping motor. During normal operation, this ring wheel is restrained and there is a synchronous movement of drive and output. For a relative angular adjustment between drive shaft and the output shaft, the ring wheel located on the drive side is rotated in one direction or the other by means of the stepping motor and a leading or trailing movement of the output shaft in relation to the drive shaft is thus obtained.
A device of this type is used, for example, in spray adjusters for diesel injection pumps. However, if it were to be used as camshaft adjuster to vary the control times of the inlet and outlet valves of internal-combustion engines, high restoring torques would occur. In such a device these torques would lead to problems with the gear teeth sets.
The object of the invention is to design an adjusting device in such a way that a continuous angular adjustment of the camshaft over a wide adjustment range can be obtained quickly and reliably.
According to the invention, the object is achieved by having an actuating element arranged freely rotatable and fixed axially on a carrier connected to the camshaft via a clamping thread and by having the carrier connected to an electric motor via a transmission means.
It is desirable that the transmission means consist of a planetary gear set, wherein the carrier forms the sun wheel of the planetary gear set. The planet wheels are arranged on a planet-wheel carrier fixedly connected in terms of rotation to the housing of the planetary gear, and the ring wheel is arranged freely rotatably in the housing of the planetary gear. The electric motor is in engagement with a ring wheel via a gear wheel fastened on its shaft.
A chain wheel is arranged on a chain-wheel carrier designed as a hollow shaft and having inner helical gear teeth and is driven by the crankshaft via a chain connection. An actuating element equipped with corresponding outer helical gear teeth is guided axially movably in the chain-wheel carrier. This actuating element is connected via inner helical gear teeth to be axially shiftably on an outer helical gear teeth surface of a flanged shaft connected firmly to the camshaft of the engine at an annular space. A carrier is mounted, via a clamping thread, to be axially shiftable on the inner part of the flanged shaft as a result of rotation. The carrier is arranged in line with the camshaft axis and receives the actuating element freely rotatable on its circumference. This carrier is connected to an electric motor via a gear.
During the normal operation of the adjusting device, that is to say in the periods when there is no relative rotation between the chain-wheel carrier and camshaft, these two shafts are connected to one another via the helical gear teeth of the actuating element and have an identical rotational speed. The carrier mounted on the inner part of the flanged shaft and receiving the actuating element, likewise has the same rotational speed because of its clamping-thread connection and transmits this rotational speed, stepped up via the gear, to rotate an electric motor.
When the electric motor is operated at a rotational speed higher or lower than this rotational speed as determined by the camshaft, it rotates the carrier arranged on the flanged shaft and thereby causes an axial shift of this carrier and of the actuating element rotatable on it. This axial shift of the actuating element gives rise to a relative rotation between the chain-wheel carrier and camshaft because of the helical gear teeth drive, and consequently to a variation of the valve control times. Accordingly, if the electric motor is operated at a higher or lower speed in relation to its speed occurring during normal operation, there is a leading or retarding adjustment of the camshaft in relation to the chain-wheel carrier, i.e. to the crankshaft. The adjusting device thus makes it possible to obtain, as a function of the speed change of the electric motor, a continuous relative rotation between crankshaft and camshaft independently of the speed range in which these shafts are operated.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.